Energized Downhole Standoff

ABSTRACT

Standoff devices and methods of their use are disclosed. In various embodiments, a standoff device includes a spring-loaded core rod whose longitudinal movement causes lateral extension members to extend outward to provide the desired standoff action. The core rod is initially restrained in its motion by a restraining part made of or including a fusible material. Melting of the fusible material causes release of the spring-loaded core rod and, as a result, outward extension of the lateral extension members. Further embodiments are described.

BACKGROUND

Downhole standoffs are used, e.g., as part of downhole tool strings, to provide a controlled radial positioning of downhole tools inside a cased borehole or open hole, preventing the tools from coming in contact with and dragging against the borehole wall and/or getting stuck, and thereby reducing wear on the tools. Standoffs currently available in the market come in different shapes, such as fins or rings, and can generally be classified into static and retractable standoffs. Static standoffs permanently increase the tool envelope and, while providing the desired spacing downhole, therefore increase the likelihood of getting the tools stuck (e.g., at surface pressure control devices) when running them in or pulling them out. Dynamic standoffs avoid this problem by being retractable. However, the motors and/or hydraulic devices used to extend and retract the standoffs downhole tend to render these standoffs delicate and, thus, prone to failure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams of example tool strings with downhole standoffs disposed in an open hole and a cased borehole, respectively, in accordance with various embodiments.

FIGS. 2A-2C are diagrams of an example standoff device in accordance with various embodiments in its initial retracted, extended, and final contracted configurations, respectively.

FIGS. 3A and 3B are diagrams of an example standoff device in accordance with various other embodiments in its initial retracted and extended configurations, respectively.

FIG. 4 is a flow chart of a method for using a standoff device with retractable lateral extension members, in accordance with various embodiments.

FIG. 5 is a flow chart of a method for using a standoff device with adjustable, but non-retractable lateral extension members, in accordance with various embodiments.

FIG. 6 is a flow chart of a method for using a standoff device configured for automatic extension at a certain borehole temperature, in accordance with various embodiments.

DESCRIPTION

Described herein are retractable standoff devices (or “standoffs”) that can be radially extended and retracted using mechanical means such as, e.g., springs in conjunction with a fusible material; also disclosed are various methods of using such standoff devices. In accordance with some embodiments, a standoff device includes one or more lateral extension members (such as, e.g., standoff arms including hinged links) that are, in the retracted configuration, spring-loaded or otherwise energized (e.g., indirectly via a spring-loaded rod to which the extension members are coupled), but prevented from extending by a restraining part made of or including the fusible material. Melting of the fusible material removes the restraint to movement, allowing the lateral extension members to extend. Subsequent retraction of the extension member(s) may be effected using a second energized spring (or other mechanical mechanism) that is likewise initially restrained by a restraining part made of or including a fusible material. Furthermore, extension (or retraction) in stages may be accomplished with a restraining part having multiple fusible sub-parts that can be melted separately and sequentially. Melting of the fusible material in the restraining parts or sub-parts may be caused by electric heating elements and a controller configured to supply current to the heating elements. Alternatively, in some embodiments, the increasing temperatures at greater depths within the borehole can be exploited to cause the fusible material to melt when the standoff device reaches a certain borehole depth. Beneficially, standoffs in accordance herewith avoid the need for motors, hydraulic mechanisms, or other delicate components, and thus afford more compact and rugged embodiments. The foregoing will be more readily understood from the following detailed description of the drawings.

FIGS. 1A and 1B are diagrams of example tool strings with downhole standoffs disposed in an open hole 100 and a cased borehole 102, respectively, in accordance with various embodiments. As shown in FIG. 1A, a tool string 104 may be lowered into the borehole 100 as part of a drill string 106, and may include multiple subs 108, 110, 112, 114 connected by joints 116. For example, tools are often integrated in the bottom hole assembly of the drill string 106 to support logging-while-drilling (LWD) operations. Alternatively, as shown in FIG. 1B, a tool string 120 (including multiple subs 122, 124, 126, 128 connected by joints 130) may be conveyed to the borehole 102 by wireline 132, slickline, or other means of conveyance, e.g., for wireline logging operations. In either scenario, standoff subs 112, 126 may be used to center (or otherwise laterally position) the tool string 104, 120 within the borehole 100, 102, using lateral extension members 134 that extend beyond the housing of the standoff subs 112, 126 and engage with the borehole wall 136 or casing 138 (e.g., via rollers 140) to provide fixed distances between the tool string 104, 120 and the borehole wall 136 or inner surface of the casing 138.

FIGS. 2A-2C are diagrams of an example standoff device 200, in accordance with various embodiments, in its initial retracted, extended, and final contracted configurations. The standoff device 200 includes lateral extension members 202 that are hinged to the body 204 (a device piece that is static with respect to the housing) of the standoff device 200 at one end and to a movable core rod 206 at the other end. In the “run in hole (RIH)” condition, the lateral extension members 202 are enclosed within the device housing 205; when engaging the borehole wall in the “standoff” condition, they extend beyond the housing 205. While two lateral extension members 202 are shown in the cross-sectional view, it should be understood that a higher number (e.g., three or four) lateral extension members 202 at different (e.g., uniformly spaced) circumferential positions may be used to achieve greater control over the lateral positioning of the tool string. Further, for certain applications, such as controlled decentralization, a single lateral extension member 202 may suffice. In the illustrated example, the lateral extension members 202 are standoff arms each including a plurality of hinged links (collectively forming a multibar linkage). Specifically, as shown, each standoff arm may include two links 208 connected to each other via a hinge 210 and a roller 212, but more links may also be used. In the standoff condition, the rollers 212 serve to engage the borehole wall or casing. Depending on the condition of the engaging surface, the rollers 212 may be made, e.g., of metal or elastomer, or even be replaced by solid stubs.

Movement of the core rod 206 along the longitudinal axis 214 of the standoff device 200 causes the lateral extension members 202 to extend or retract. When the core rod 206 moves in a first direction (downward in the illustrated example), the lateral extension members 202 fold to extend laterally outward, as shown in FIG. 2B. The rollers 212 can then engage with the borehole wall or casing to provide the desired standoff action. When the core rod 206 moves in a second, opposite direction (upward in the illustrated example), the lateral extension members 202 straighten out to retract laterally inward, as shown in FIG. 2C. For ease of reference throughout the following description, the standoff device 200 is assumed to be oriented in the borehole such that the first direction, which causes extension of the lateral extension members 202, is the downward direction. It should be understood, however, that the standoff device 200 could alternatively be oriented in the opposite way, such that upward movement of the core rod 206 results in lateral extension of the lateral extension members 202. In this case, designations such as “upward,” “downward,” “top,” and “bottom” used in the following description are to be reversed.

Movement of the core rod 206 in either direction may be caused by initially energized springs (e.g., compression springs, coil springs, wave springs, or other types of springs). Referring to FIG. 2A, a compressed engaging spring 216 is placed adjacent a radially or laterally protruding head 218 of the core rod 206 at the upper end of the core rod 206, exerting a force in the first direction (downward) onto the core rod 206. The head 218 is integrally formed with or fixedly attached to the core rod 206, but has a larger lateral dimension (e.g., diameter) than the remainder of the core rod 206, such that it provides a bottom surface against which a restraining part or “spacer” 220 can be placed to initially restrain downward movement of the core rod 206. The spacer 220, engaging spring 216, and core rod head 218 sandwiched therebetween are enclosed in a cage 222. The spacer 220 includes or consists of a fusible material that is solid (and can take compression forces if suitably packed) up to a certain temperature, and melts beyond that temperature. Suitable fusible materials include alloys (e.g., tin-silver alloys), which can be custom-made to achieve a desired melting temperature. The spacer 220 can be caused to melt, e.g., by application of an electric current to one or more electric heater elements 224 adjacent the spacer 220. The heater element(s) 224 may be connected to a control unit 226 that is, in turn, connected to the tool string and controlled from the surface. The melted spacer material is pushed out of the way, and may re-solidify along the periphery or on the other side of the core rod head 218. Alternatively, the standoff device 200 may be configured to allow the melted material to be pushed out into the well. Upon melting of the spacer 220, the core rod 206 moves downward, as shown in FIG. 2B, due to the force exerted by the extending engaging spring 216, pushing the lateral extension members 202 out of the housing 205. The outer diameter of the standoff device 200 in the fully extended configuration is determined by the width of the fusible spacer 220, which controls the stroke of the core rod 206, and the length of the links 208 in the standoff arms. The strength of the engaging spring 216 can be adjusted to achieve the desired radial support.

To facilitate retraction of the lateral extension members 202, the standoff device 200 further includes an initially compressed return spring 227 (see FIGS. 2A and 2B) that is placed adjacent the bottom surface of the cage 222 and exerts an upward force on the cage 222. Movement of the cage 222 is, however, initially restricted by a second restraining part or spacer 228 placed above the cage 222. The cage 222 is, thus, energized by the return spring 227 on one side and bound by the second spacer 228 on the other side. The second spacer 228, like the first spacer 220, includes or consists of a fusible material, which, when melted, can re-solidify along the periphery or on the other side of the cage 222 or be pushed out of the housing 205. Melting the fusible material (e.g., by applying an electric current to one or more electric heating elements 230 adjacent the spacer 228) causes release of the return spring 227, which then pushes the cage 222, and with it the core rod head 218, upward. This causes the core rod 206 in its entirety to move upward, retracting the lateral extension members 202 back into the housing 205, as shown in FIG. 2C. If the width of the second spacer 228 equals that of the first spacer 220, the core rod 206 moves back into its original position and the lateral extension members 202 are fully retraced.

The standoff device 200 further includes, at the ends of its housing 205, joints 232 for connecting the device 200 to other tools, thereby integrating it as a sub into a tool string (e.g., tool string 104 or 120 shown in FIGS. 1A or 1B, respectively). The standoff device 200 is centrally hollowed out to provide for a wire feedthrough 234, allowing the device 200 to be placed at any point in the tool string. Positional sensors may be included, e.g., affixed to the housing 205 and the core rod 206, to determine the operational state of the standoff device 200, e.g., whether the device 200 is in the retracted or extended configuration. The sensor information may be provided as feedback to the control unit 226, and from there to the surface. For example, the sensor information may serve to confirm that the standoff arms are fully retracted before the tool string is pulled out of the borehole.

In some embodiments, multiple standoff devices 200 are used in a tool string. For example, multiple standoffs 200 spaced apart throughout a long tool string may improve centering the tool string. Multiple standoffs 200 used in conjunction with high-stiffness springs may even allow for lifting the standoff 200, and with it the tool string, off the borehole wall in a horizontal borehole section.

Various modifications of the standoff device 200 depicted in FIGS. 2A-2C can be implemented. For example, restraining parts may include multiple stacked spacers (constituting sub-parts of the restraining parts) each having its own associated electric heating element. This allows melting off spacers progressively, leading to multiple strokes of the core rod 206 and thereby providing multiple standoff diameters.

Further, the lateral extension members may be implemented by structures other than hinged linkages. FIGS. 3A and 3B, for example, illustrate a standoff device 300 in the initial retracted and extended configuration, respectively, that includes a wedge mechanism for providing the retractable standoff. One or more inner wedges 302 integrated with the core rod 304 (e.g., manufactured in one piece with the core rod 304, or fixedly attached to the core rod 304) engage one or more outer wedges 306 that constitute the lateral extension members. As the core rod 304 moves downward (as depicted) along the longitudinal tool axis, the inner wedge(s) 302 push(es) the outer wedge(s) 306 outward beyond the housing 205. As the core rod 304 moves back upward, retracting the inner wedge(s) 302 with it, the outer wedge(s) 306 can move back inward, e.g., as a result of one or more springs (not shown) used to bias them towards the inner position and/or borehole pressures that push them inward. The inner and outer wedges 302, 306 may be radially symmetric about the longitudinal axis, forming a single conically shaped inner wedge 302 and a single outer wedge 306 defining a conical cavity conforming to the inner wedge 302. Alternatively, multiple fin-like inner and outer wedges 302, 306 may be distributed circumferentially about the core rod 304. It is also possible to combine a single conical inner wedge 302 with multiple fin-like outer wedges 306 (or vice versa). Depending on the type of outer wedge 306, the outer wedge(s) 306 may contact the borehole wall at discrete (point-like) locations, along lines, or across a surface area.

FIG. 4 is a flow chart of a method 400 for using standoff devices with retractable lateral extension members, as described above. Active acts are indicated with sharp rectangles, whereas acts that result automatically by operation of the standoff device are depicted with rounded corners. The method 400 involves running a standoff device (e.g., standoff device 200, 300) into a borehole as part of a tool string, the standoff device being in the RIH condition (with lateral extension members in the contracted configuration) (act 402). The standoff device has fusible restraining parts with melting temperatures that exceed the expected borehole temperatures. When the tool string has reached a desired location within the borehole where the standoff is to be activated, an electric current is caused to be applied to the electric heater element(s) 224 adjacent the fusible restraining part (e.g., spacer 220) associated with the engaging spring 216, e.g., by transmitting a suitable control signal downhole to the control unit 226 (act 404). This causes the restraining part to melt, the engaging spring to push the core rod 206, and the lateral extension members 202 to extend and engage the borehole wall or casing (act 406). In preparation for retrieving the tool string, an electric current is caused to be applied to the electric heater element(s) 230 adjacent the fusible restraining part (e.g., the second spacer 228) associated with the return spring 227, e.g., by transmitting a second suitable control signal downhole to the control unit 226 (act 408). This causes the second restraining part to melt, the return spring to move the core rod 206 in the reverse direction, and the lateral extension members 202 to retract (act 410). With the standoff device again in the retracted configuration, the tool string can then be retrieved (act 412).

In one embodiment, a standoff device with adjustable standoff diameter is configured for a specific desired standoff diameter at the surface and thereafter not further altered. In this case, the return spring and associated spacer may be omitted from the standoff device. Further, the device need not include electric heating elements and a control unit, as an external heater may be used to melt the fusible restraining part adjacent the engagement spring. The restraining part may be melted fully or only partially, depending on the desired standoff diameter. Re-solidification of the melted material may serve to lock the lateral extension members in place. (For this purpose, a material whose melting temperature is higher than the expected downhole temperatures is selected.)

FIG. 5 is a flow chart of a method 500 for using such standoff devices with adjustable, but non-retractable lateral extension members. The method 500 involves heating a fusible restraining part associated with the engaging spring at the surface (act 502) to cause it to melt at least partially such that the lateral extension members extend to the desired standoff diameter (act 504), and then allowing the melted material to cool (act 506) to lock the lateral extension members in place (508). The standoff device is then run into the borehole, in its extended configuration, as part of a tool string (act 510), and subsequently retrieved in the same configuration (act 512).

In yet another embodiment, a standoff device is configured to automatically extend at a certain borehole depth by virtue of selecting or creating a fusible material for the restraining part that has a melting temperature corresponding to that depth. For example, the composition of a metal alloy used for the fusible material can be adjusted to achieve the desired melting temperature. No heating elements are needed in this device, nor does the device include a return spring and associated restraining part. The standoff device is run into the borehole in the retracted position, locked in place by the fusible restraining part. Once the device reaches the certain borehole depth, the elevated borehole temperature melts the fusible material, and the engaging spring causes the lateral extension members to extend. The device remains in the extended configuration until reset at the surface.

FIG. 6 is a flow chart of a method 600 for using a standoff device configured for automatic extension at a certain borehole temperature. The method 600 involves running the device, as part of a tool string, in the borehole in its RIH condition, i.e., with retracted lateral extension members (act 602). The device is then lowered to a borehole depth at which the borehole temperature exceeds the melting temperature of the fusible material of the restraining part (act 604). This causes the restraining part to melt and release the engaging spring, and the lateral extension members to extend and engage the borehole wall or casing (act 606). Thereafter, the tool string with the standoff device in its extended configuration can be retrieved from the borehole (act 608).

The following numbered examples are illustrative embodiments:

1. A standoff device comprising: a spring-loaded core rod disposed along a longitudinal axis of the standoff tool and configured to move longitudinally in a first direction upon release; a (first) restraining part formed at least in part from fusible material and restraining movement of the spring-loaded core rod, such that melting of the fusible material causes release of the spring-loaded core rod; and one or more lateral extension members coupled to the core rod and configured to extend laterally outward upon longitudinal movement of the core rod in the first direction.

2. The device of example 1, wherein the one or more lateral extension members comprise one or more standoff arms hinged to the core rod, each standoff arm comprising a plurality of hinged links.

3. The device of example 1, wherein the one or more lateral extension members comprise an outer wedge engaging an inner wedge integrated with the core rod.

4. The device of any preceding example, further comprising an electric heating element adjacent the restraining part and a controller configured to supply current to the heating element.

5. The device of any preceding example, wherein the first restraining part comprises a plurality of sub-parts each having its own associated electric heating element.

6. The device of any preceding example, further comprising a return spring initially restrained in its motion by a second restraining part comprising a fusible material, melting of the fusible material of the second restraining part causing release of the return spring, the return spring upon release causing the core rod to move longitudinally in a second direction opposite the first direction.

7. The device of example 6, further comprising an electric heating element adjacent the second restraining part and a controller configured to supply current to the heating element.

8. The device of example 6, wherein the spring-loaded core rod comprises a head placed between an engaging spring and the first restraining part, the tool further comprising a cage enclosing the engaging spring, the head, and the restraining part, the cage being placed between the return spring and the second restraining part.

9. The device of any preceding example, wherein the fusible material has a melting temperature corresponding to a specified downhole temperature.

10. The device of any preceding example, defining a central hollow core along the longitudinal tool axis.

11. The device of any preceding example, further comprising a housing including, at its ends, joints for integrating the standoff device into a tool string.

12. The device of any preceding example, further comprising one or more positional sensors for determining an operational state of the device.

13. A method of using a standoff device, the method comprising: disposing the standoff device in a borehole; and causing a fusible material associated with a restraining part of the standoff device to melt so as to release a spring-loaded core rod, thereby causing one or more lateral extension members to extend laterally from the standoff device into contact with a wall of the borehole.

14. The method of example 13, wherein causing the fusible material to melt comprises causing an electrical current to be applied to an electric heating element adjacent the fusible material.

15. The method of example 14, further comprising transmitting a control signal downhole to the standoff device, the electric current being applied in response to the control signal.

16. The method of any of examples 13-15, further comprising causing a fusible material associated with a second restraining part initially restraining motion of a return spring to melt so as to release the return spring, release of the return spring causing the core rod to move so as to retract the one or more lateral extension members.

17. The method of example 16, further comprising retrieving the standoff device from the borehole following retraction of the one or more lateral extension members.

18. The method of example 13, wherein the fusible material is caused to melt prior to disposing the standoff device in the borehole.

19. The method of example 13, wherein causing the fusible material to melt comprises lowering the standoff device to a depth at which a borehole temperature exceeds a melting temperature of the fusible material.

20. The method of any of examples 13-15, wherein the fusible material is caused to melt when the device is located in a horizontal borehole section, extension of the one or more lateral extension members causing lifting of the standoff device off a borehole wall.

21. The method of any of examples 13-20, wherein the standoff device is placed in-line with a tool string.

Many variations may be made in the devices, and techniques described and illustrated herein without departing from the scope of the inventive subject matter. Accordingly, the described embodiments are not intended to limit the scope of the inventive subject matter. Rather, the scope of the inventive subject matter is to be determined by the scope of the following claims and all additional claims supported by the present disclosure, and all equivalents of such claims. 

What is claimed is:
 1. A standoff device comprising: a spring-loaded core rod disposed along a longitudinal axis of the standoff device and configured to move longitudinally in a first direction upon release; a restraining part formed at least in part from fusible material and restraining movement of the spring-loaded core rod, such that melting of the fusible material causes release of the spring-loaded core rod; and one or more lateral extension members coupled to the core rod and configured to extend laterally outward upon longitudinal movement of the core rod in the first direction.
 2. The device of claim 1, wherein the one or more lateral extension members comprise one or more standoff arms hinged to the core rod, each standoff arm comprising a plurality of hinged links.
 3. The device of claim 1, wherein the one or more lateral extension members comprise an outer wedge engaging an inner wedge integrated with the core rod.
 4. The device of claim 1, further comprising an electric heating element adjacent the restraining part and a controller configured to supply current to the heating element.
 5. The device of claim 4, wherein the first restraining part comprises a plurality of sub-parts each having its own associated electric heating element.
 6. The device of claim 1, further comprising a return spring initially restrained in its motion by a second restraining part comprising a fusible material, melting of the fusible material of the second restraining part causing release of the return spring, the return spring upon release causing the core rod to move longitudinally in a second direction opposite the first direction.
 7. The device of claim 6, further comprising an electric heating element adjacent the second restraining part and a controller configured to supply current to the heating element.
 8. The device of claim 6, wherein the spring-loaded core rod comprises a head placed between an engaging spring and the restraining part, the tool further comprising a cage enclosing the engaging spring, the head, and the restraining part, the cage being placed between the return spring and the second restraining part.
 9. The device of claim 1, wherein the fusible material has a melting temperature corresponding to a specified downhole temperature.
 10. The device of claim 1, defining a central hollow core along the longitudinal tool axis.
 11. The device of claim 1, further comprising a housing including, at its ends, joints for integrating the standoff device into a tool string.
 12. The device of claim 1, further comprising one or more positional sensors for determining an operational state of the device.
 13. A method of using a standoff device, the method comprising: disposing the standoff device in a borehole; and causing a fusible material associated with a restraining part of the standoff device to melt so as to release a spring-loaded core rod, thereby causing one or more lateral extension members to extend laterally from the standoff device into contact with a wall of the borehole.
 14. The method of claim 13, wherein causing the fusible material to melt comprises causing an electrical current to be applied to an electric heating element adjacent the fusible material.
 15. The method of claim 14, further comprising transmitting a control signal downhole to the standoff device, the electric current being applied in response to the control signal.
 16. The method of claim 13, further comprising causing a fusible material associated with a second restraining part initially restraining motion of a return spring to melt so as to release the return spring, release of the return spring causing the core rod to move so as to retract the one or more lateral extension members.
 17. The method of claim 16, further comprising retrieving the standoff device from the borehole following retraction of the one or more lateral extension members.
 18. The method of claim 13, wherein the fusible material is caused to melt prior to disposing the standoff device in the borehole.
 19. The method of claim 13, wherein causing the fusible material to melt comprises lowering the standoff device to a depth at which a borehole temperature exceeds a melting temperature of the fusible material.
 20. The method of claim 13, wherein the fusible material is caused to melt when the device is located in a horizontal borehole section, extension of the one or more lateral extension members causing lifting of the standoff device off a borehole wall.
 21. The method of claim 13, wherein the standoff device is placed in-line with a tool string. 